Footprints of speciation and hybridization in the genomes of Galápagos iguanas

火山岛可以被视为进化的“天然实验室”，因为许多重要的进化过程可以在比大陆环境更简单的条件下观察和重建。在这些岛屿上发生的主要进化过程之一是物种的到达和随后的进化，这些岛屿通常由有限数量的创始人个体代表。到达后，物种必须适应新的环境条件，这往往导致新物种的进化，有时甚至是物种的整个适应辐射。加拉帕戈斯群岛可能是最著名的纯海洋火山岛，拥有特有物种，其中一些成为进化生物学的教科书范例。在1000多万年前到达群岛后，南美洲蜥蜴的一个谱系在加拉帕戈斯群岛上多样化为陆地（Conolophus属）和海洋鬣蜥（Amblyrhynchus属）。与世界上其他蜥蜴不同的是，海鬣蜥已经完全适应了海洋环境。此外，海洋鬣蜥的各种岛屿种群提供了一个独特的系统来研究两个主要的进化力量的影响-当地适应/物种形成与杂交。通过对来自南美大陆的加拉帕戈斯鬣蜥及其姐妹类群（Cachryx属和Ctenosaura属的物种）的基因组进行测序，我们将分别解开加拉帕戈斯鬣蜥分歧的基因组特征以及随后的陆地和海洋鬣蜥分化。这将使我们能够确定当物种在岛屿上面临新的环境条件时通常处于选择状态的基因组区域（基因），更具体地说，是蜥蜴物种对海洋环境独特适应的基础基因。海洋和陆地鬣蜥的完整参考基因组的基础上，我们将进一步测试我们的假设，当地的适应和杂交的结果到一个共同的物种基因库的海洋鬣蜥通过经常性的杂交事件的适应在当地的基因组等价物的整合。这一过程将增强一个物种的进化潜力。我们将遵循我们的假设，首先进行当地的实地研究，这提供了一个当前的洞察力的过程中，当地的适应和杂交的圣克里斯托瓦尔岛。第二，通过将这一快照的见解整合到一个更广泛的进化框架中，我们将分析这两种影响对人口基因组学以及转录组学/蛋白质组学水平的后果。要做到这一点，我们将包括岛屿种群的海洋鬣蜥代表低覆盖率的基因组和转录谱。观察到的基因组模式将被发现的加拉帕戈斯陆鬣蜥，其中系统发育的分歧（物种形成）没有杂交的模式进行比较是明显的进化时间尺度上。

Volcanic islands can be seen as “natural laboratories” of evolution as many important evolutionary processes can be observed and reconstructed under simpler conditions compared to mainland settings. One of the major evolutionary processes that take place on such islands, is the arrival and subsequent evolution of species on islands usually represented by a limited number of founder individuals. Following arrival, species have to adapt to new environmental conditions often resulting into the evolution of new species and sometimes entire adaptive radiations of species. The Galápagos archipelago is probably the most famous setting of purely oceanic volcanic islands with endemic species, some of which became textbook examples of evolutionary biology. Having arrived more than 10 million years ago on the archipelago, a lineage of South-American lizards diversified on the Galápagos archipelago into land (genus Conolophus) and marine iguanas (genus Amblyrhynchus). Like no other lizard worldwide, marine iguanas have fully adapted to the marine environment. Moreover, the various island populations of marine iguanas provide a unique system to study the effects of two major evolutionary forces – local adaptation/speciation versus hybridization. By sequencing the genomes of Galápagos iguanas and their sister taxa from the South-American mainland (species of the genera Cachryx and Ctenosaura), we will unravel genomic signatures of the divergence of Galápagos iguanas and the subsequent differentiation of land and marine iguanas, respectively. This will allow us to identify genomic regions (genes) that are in general under selection when species face new environmental conditions on islands and more specific, genes that underlie the unique adaptation of a lizard species to the marine environment. Based on the full reference genomes of marine and land iguanas, we will further test our hypothesis that local adaptation and hybridization result into the integration of the genomic equivalents of adaptations on a local level into a common species gene pool of the marine iguana by recurrent hybridization events. Such a process would enhance the evolutionary potential of a species. We will follow up our hypothesis by first conducting a local field study, which provides a current insight on the processes of local adaptation and hybridization on the island of San Cristóbal. Second, by integrating the insights from this snapshot into a broader evolutionary framework, we will analyse the consequences of both effects on a population genomics as well as transcriptomic/proteomic level. To do so, we will include island populations of the marine iguana represented by low coverage genomes and transcriptomic profiles. Observed genomic patterns will be compared with patterns found for the system of the Galápagos land iguanas, in which phylogenetic divergence (speciation) without hybridization is evident on an evolutionary time scale.